Biscarbazole derivative host materials for oled emissive region

ABSTRACT

An organic electroluminescence device utilizes a novel combination of one or more biscarbazole derivative compounds as the phosphorescent host material in combination with an organometallic phosphorescent material as a dopant in the light emitting region of the device, where the biscarbazole derivative compounds are represented by a formula (1A) or (2A) below: (1A), (2A) where A 1  represents a substituted or unsubstituted nitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms; A 2  represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 ring carbon atoms, or substituted or unsubstituted nitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms; X i  and X 2  each are a linking group; Y 1  to Y 4  each represent a substituent; p and q represent an integer of 1 to 4; and r and s represent an integer of 1 to 3; and the organometallic phosphorescent material is a compound having a substituted chemical structure represented by the formula (4A): where each R is independently selected from the group consisting of H, alkyl, alkenyl, alkynyl, alkylaryl, CN, CF 3 , C n F 2n+1 , trifluorovinyl, CO 2 R, C(O)R, NR 2 , NO 2 , OR, halo, aryl, heteroaryl, substituted aryl, substituted heteroaryl or a heterocyclic group; M is a platinum group metal; Ar′, Ar″, Ar′″ and Ar″″ each independently represent a substituted or unsubstituted aryl or heteroaryl substituent on the phenylpyridine ligand; a is 0 or 1; b is 0 or 1; c is 0 or 1; d is 0 or 1; m is 1 or 2; n is 1 or 2; m+n is the maximum number of ligands that can be coordinated to M, and wherein at least one of a, b, c, and d is 1 and when at least one of a and b is 1 and at least one of b and c is 1, at least one of Ar′ and Ar″ is different from at least one of Ar′″ and Ar″″.

BACKGROUND OF THE INVENTION

The present invention relates to an organic electroluminescent (EL)device such as an organic light emitting device (hereinafter abbreviatedas an OLED) and materials capable of being used in such an OLED. Inparticular, it relates to an OLED which comprises a light emitting layerwhich emits a green light, and materials for an OLED which are used forthe same.

RELATED ART

OLEDs which comprise an organic thin film layer which includes a lightemitting layer located between an anode and a cathode are known in theart. In such devices, emission of light may be obtained from excitonenergy, produced by recombination of a hole injected into a lightemitting layer with an electron.

Generally, OLEDs are comprised of several organic layers in which atleast one of the layers can be made to electroluminesce by applying avoltage across the device. When a voltage is applied across a device,the cathode effectively reduces the adjacent organic layers (i.e.,injects electrons), and the anode effectively oxidizes the adjacentorganic layers (i.e., injects holes). Holes and electrons migrate acrossthe device toward their respective oppositely charged electrodes. When ahole and electron meet on the same molecule, recombination is said tooccur, and an exciton is formed. Recombination of the hole and electronin luminescent compounds is accompanied by radiative emission, therebyproducing electroluminescence.

Depending on the spin states of the hole and electron, the excitonresulting from hole and electron recombination can have either a tripletor singlet spin state. Luminescence from a singlet exciton results influorescence, whereas luminescence from a triplet exciton results inphosphorescence. Statistically, for organic materials typically used inOLEDs, one quarter of the excitons are singlets, and the remainingthree-quarters are triplets (see, e.g., Baldo, et al., Phys. Rev. B,1999, 60, 14422). Until the discovery that there were certainphosphorescent materials that could be used to fabricate practicalelectro-phosphorescent OLEDs (U.S. Pat. No. 6,303,238) and,subsequently, demonstration that such electro-phosphorescent OLEDs couldhave a theoretical quantum efficiency of up to 100% (i.e., harvestingall of both triplets and singlets), the most efficient OLEDs weretypically based on materials that fluoresced. Fluorescent materialsluminesce with a maximum theoretical quantum efficiency of only 25%(where quantum efficiency of an OLED refers to the efficiency with whichholes and electrons recombine to produce luminescence), since thetriplet to ground state transition of phosphorescent emission isformally a spin forbidden process. Electro-phosphorescent OLEDs have nowbeen shown to have superior overall device efficiencies as compared withelectro-fluorescent OLEDs (see, e.g., Baldo, et al., Nature, 1998, 395,151 and Baldo, et al., Appl. Phys. Lett. 1999, 75(3), 4).

Due to strong spin-orbit coupling that leads to singlet-triplet statemixing, heavy metal complexes often display efficient phosphorescentemission from such triplets at room temperature. Accordingly, OLEDscomprising such complexes have been shown to have internal quantumefficiencies of more than 75% (Adachi, et al., Appl. Phys. Lett., 2000,77, 904). Certain organometallic iridium complexes have been reported ashaving intense phosphorescence (Lamansky, et al., Inorganic Chemistry,2001, 40, 1704), and efficient OLEDs emitting in the green to redspectrum have been prepared with these complexes (Lamansky, et al., J.Am. Chem. Soc., 2001, 123, 4304). Phosphorescent heavy metalorganometallic complexes and their respective devices have been thesubject of U.S. Pat. Nos. 6,830,828 and 6,902,830; U.S. Publications2006/0202194 and 2006/0204785; and U.S. Pat. Nos. 7,001,536; 6,911,271;6,939,624; and 6,835,469.

OLEDs, as described above, generally provide excellent luminousefficiency, image quality, power consumption and the ability to beincorporated into thin design products such as flat screens, andtherefore hold many advantages over prior technology, such as cathoderay devices.

However, improved OLEDs, including, for example, the preparation ofOLEDs having greater current efficiency are desirable. In this regard,light emitting materials (phosphorescent materials) have been developedin which light emission is obtained from a triplet exciton in order toenhance internal quantum efficiency.

As discussed above, such OLEDs can have a theoretical internal quantumefficiency up to 100% by using such phosphorescent materials in thelight emitting layer (phosphorescent layer), and the resulting OLED willhave a high efficiency and low power consumption. Such phosphorescentmaterials may be used as a dopant in a host material which comprisessuch a light emitting layer.

In a light emitting layer formed by doping with a light emittingmaterial such as a phosphorescent material, excitons can efficiently beproduced from a charge injected into a host material. Exciton energy ofan exciton produced may be transferred to a dopant, and emission may beobtained from the dopant at high efficiency. Exitons may be formedeither on the host materials or directly on the dopant.

In order to achieve intermolecular energy transfer from a host materialto a phosphorescent dopant with high device efficiencies, the excitedtriplet energy EgH of the host material must be greater than the excitedtriplet energy EgD of the phosphorescent dopant.

In order to carry out intermolecular energy transfer from a hostmaterial to a phosphorescent dopant, an excited triplet energy Eg (T) ofthe host material has to be larger than an excited triplet energy Eg (S)of the phosphorescent dopant.

CBP (4,4′-bis(N-carbazolyl)biphenyl) is known to be a representativeexample of a material having an efficient and large excited tripletenergy. See, e.g., U.S. Pat. No. 6,939,624. If CBP is used as a hostmaterial, energy can be transferred to a phosphorescent dopant having aprescribed emission wavelength, such as green, and an OLED having a highefficiency can be obtained. When CBP is used as a host material, theluminous efficiency is notably enhanced by phosphorescent emission.However, CBP is known to have a very short lifetime, and therefore it isnot suitable for practical use in EL devices such as an OLED. Withoutbeing bound by scientific theory, it is believed that this is becauseCBP may be heavily deteriorated by a hole due to its oxidative stabilitynot being high, in terms of molecular structure.

International Patent Application Publication WO 2005/112519 discloses atechnique in which a condensed ring derivative having anitrogen-containing ring such as carbazole and the like is used as ahost material for a phosphorescent layer showing green phosphorescence.The current efficiency and the lifetime are improved by the abovetechnique, but it is not satisfactory in a certain case for practicaluse.

On the other hand, a wide variety of host materials (fluorescent hosts)for a fluorescent dopant showing fluorescent emission are known, andvarious host materials can be proposed which, by combination with afluorescent dopant, may form a fluorescent layer which exhibitsexcellent luminous efficiency and lifetime.

In a fluorescent host, an excited singlet energy Eg (S) is larger thanin a fluorescent dopant, but an excited triplet energy Eg (T) of such ahost is not necessarily larger. Accordingly, a fluorescent host cannotsimply be used in place of a phosphorescent host as a host material toprovide a phosphorescent emitting layer.

For example, anthracene derivatives are known well as a fluorescenthost. However, an excited state triplet energy Eg (T) of anthracenederivatives may be as small as about 1.9 eV. Thus, energy transfer to aphosphorescent dopant having an emission wavelength in a visible lightregion of 500 nm to 720 nm cannot be achieved using such a host, sincethe excited state triplet energy would be quenched by a host having sucha low triplet state energy. Accordingly, anthracene derivatives areunsuitable as a phosphorescent host.

Perylene derivatives, pyrene derivatives and naphthacene derivatives arenot preferred as phosphorescent hosts for the same reason.

The use of aromatic hydrocarbon compounds as phosphorescent hosts isdisclosed in Japanese Patent Application Laid-Open No. 142267/2003. Thatapplication discloses phosphorescent host compounds with a benzeneskeleton core and with two aromatic substituents bonded at metapositions.

However, the aromatic hydrocarbon compounds described in Japanese PatentApplication Laid-Open No. 142267/2003 assume a rigid molecular structurehaving a good symmetric property and provided with five aromatic ringsin which molecules are arranged in a bilaterally symmetrical mannertoward a central benzene skeleton. Such an arrangement has the drawbackof a likelihood of crystallization of the light emitting layer.

On the other hand, OLEDs in which various aromatic hydrocarbon compoundsare used are disclosed in International Patent Application PublicationsWO 2007/046685; Japanese Patent Application Laid-Open No. 151966/2006;Japanese Patent Application Laid-Open No. 8588/2005; Japanese PatentApplication Laid-Open No. 19219/2005; Japanese Patent ApplicationLaid-Open No. 19219/2005; and Japanese Patent Application Laid-Open No.75567/2004. However, the efficiency of these materials as aphosphorescent host is not disclosed.

In addition, OLEDs prepared by using various fluorene compounds aredisclosed in Japanese Patent Application Laid-Open No. 043349/2004;Japanese Patent Application Laid-Open No. 314506/2007; and JapanesePatent Application Laid-Open No. 042485/2004. However, the effectivenessof these materials as a phosphorescent host is not disclosed.

Further, Japanese Patent Application Laid-Open No. 042485/2004 discloseshydrocarbon compounds in which a condensed polycyclic aromatic ring isbonded directly to a fluorene ring. However, the effectiveness of anOLED prepared by combining such materials with a phosphorescent materialis not disclosed, and the application discloses perylene and pyrenerings which are known to have a small triplet energy level as condensedpolycyclic aromatic rings, and which are not preferred for use as alight emitting layer of a phosphorescent device, and materials which areeffective for a phosphorescent device are not selected.

Despite the recent advancements in OLED technology, there remains a needfor host materials which can transfer energy to a phosphorescentmaterial with high efficiency and with an extended lifetime.

SUMMARY OF THE INVENTION

One embodiment of the present disclosure provides an organicelectroluminescence device such as an OLED that utilizes a novelcombination of biscarbazole derivative compound as a host compound inthe light emitting region of the device and an organometallicphosphorescent material as a dopant in the light emitting region of thedevice. The organic electroluminescence device of the present disclosurecomprises a cathode, an anode, and a plurality of organic thin-filmlayers provided between the cathode and the anode. At least one of theorganic thin-film layers is an emitting layer comprising aphosphorescent material and a host material that is a biscarbazolederivative compound represented by a formula (1A) or (2A) below:

where A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 carbon atoms forming a ring;

A₂ represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, or substituted or unsubstitutednitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms;

X₁ and X₂ each independently represents substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3; and

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different. Thephosphorescent material is an organometallic compound having asubstituted chemical structure represented by the following formula(4A):

where each R is independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl, heteroaryl,substituted aryl, substituted heteroaryl or a heterocyclic group;

M is a platinum group metal;

Ar′, Ar″, Ar′″ and Ar″″ each independently represent a substituted orunsubstituted aryl or heteroaryl substituent on the phenylpyridineligand;

a is 0 or 1;b is 0 or 1;c is 0 or 1;d is 0 or 1;m is 1 or 2;n is 1 or 2;m+n is the maximum number of ligands that can be coordinated to M, andwherein at least one of a, b, c, and d is 1 and when at least one of aand b is 1 and at least one of b and c is 1, at least one of Ar′ and Ar″is different from at least one of Ar′″ and Ar″″.

In another embodiment, the organic electroluminescence device comprisesa cathode, an anode, and a plurality of organic thin-film layersprovided between the cathode and the anode, wherein at least one of theorganic thin-film layers is an emitting layer comprising a pair ofco-host materials and a phosphorescent material. A first host materialof the pair of co-host materials is a biscarbazole derivative compoundrepresented by a formula (1A) below:

where A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms;

A₂ represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, or substituted or unsubstitutednitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms;

X₁ and X₂ each independently represents substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3;

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different. Asecond host material of the pair of co-host materials is a biscarbazolederivative compound represented by a formula (2A) below:

where X₂ represents a single bond, substituted or unsubstituted aromatichydrocarbon group having 6 to 30 ring carbon atoms, substituted orunsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3; and

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different.

In another embodiment, an organic electroluminescence device comprises acathode, an anode, and a plurality of organic thin-film layers providedbetween the cathode and the anode, wherein at least one of the organicthin-film layers is an emitting layer comprising a pair of co-hostmaterials and a phosphorescent material. A first host material of thepair of co-host materials is a biscarbazole derivative compoundrepresented by a formula (1A) below:

where A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms;

A₂ represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, or substituted or unsubstitutednitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms;

X₁ and X₂ each are independently represents substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3;

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different. Asecond host material of the pair of co-host materials is a biscarbazolederivative compound represented by a formula (3A) below:

where G is substituted or unsubstituted aryl group having 6 to 40 carbonatoms, or represented by a formula 3(b) below:

in formula 3(b), * represents link with L³;in formula (3A), X₁ is sulfur atom or represents N—R⁹;in formula 3(b), X₂ is sulfur atom or represents N—R¹⁰;

R¹ to R⁸ each represent independently an alkyl group having 1 to 5carbon atoms, substituted or unsubstituted cycloalkyl group having 3 to6 carbon atoms, substituted or unsubstituted alcoxy group having 1 to 5carbon atoms, substituted or unsubstituted cycloalkoxy group having 3 to6 carbon atoms, substituted or unsubstituted aryl group having 6 to 18carbon atoms, substituted or unsubstituted aryloxy group having 6 to 18carbon atoms, substituted or unsubstituted heteroaryl group having 5 to18 carbon atoms, substituted by alkyl group having 1 to 5 carbon atomsor unsubstituted amino group, substituted by alkyl group having 1 to 6carbon atoms or unsubstituted silyl group, a fluoro group or a cyanogroup. R¹ to R⁸ being optionally bonded to each other to form a ringstructure;

when G or R¹ to R⁸ have a substituent, R each represent independently analkyl group having 1 to 5 carbon atoms, cycloalkyl group having 3 to 6carbon atoms, alcoxy group having 1 to 4 carbon atoms, cycloalkoxy grouphaving 3 to 6 carbon atoms, aryl group having 6 to 18 carbon atoms,aryloxy group having 6 to 18 carbon atoms, heteroaryl group having 5 to18 carbon atoms, substituted by alkyl group having 1 to 5 carbon atomsor unsubstituted amino group, substituted by alkyl group having 1 to 6carbon atoms or unsubstituted silyl group, a fluoro group or a cyanogroup;

a, d and f each represent independently an integer of any of 0 to 4, andb, c and e each represent independently an integer of any of 0 to 3; asum of a to f is 4 or less;

R⁹ to R¹⁰ each represent independently an alkyl group having 1 to 5carbon atoms, phenyl group, toluyl group, dimethyl phenyl group,trimethyl phenyl group, biphenyl group, dibenzofuranyl group ordibenzothiophenyl group;

g represents an integer of any of 0 to 3, and h represents an integer ofany of 0 to 4; a sum of g and h is 4 or less;

provided that when X¹ and X² are nitrogen, and R⁹ is phenyl group, R¹⁰is not phenyl group;

-   -   L¹ represents a single bond, a divalent linkage group containing        N, a divalent linkage group containing O, a divalent linkage        group containing Si, a divalent linkage group containing P, a        divalent linkage group containing S, an alkylene group having 1        to 5 carbon atoms, cycloalkylene group having 3 to 6 carbon        atoms, arylene group having 6 to 18 carbon atoms or        heteroarylene group having 5 to 18 carbon atoms;

L² and L³ each represent independently a single bond, an alkylene grouphaving 1 to 5 carbon atoms, cycloalkylene group having 3 to 6 carbonatoms, arylene group having 6 to 18 carbon atoms or heteroarylene grouphaving 5 to 18 carbon atoms; and

L¹ to L³ may be further substituted with the substituent R describedabove; provided that when L¹ is an arylene group or a heteroarylenegroup, a and d each represent independently an integer of any of 1 to 4.

The inventors have found that the organic EL devices containing the hostmaterials and phosphorescent materials according to the presentdisclosure exhibit low voltage requirement with high luminousefficiency. Additionally, the devices having the co-host combinations inthe emitting layer according to the present disclosure exhibited anadditional benefit of improved life time of more than 3 times whencompared to a single-host example device.

A luminous efficiency and a lifetime of the multilayered organic ELdevice depend on a carrier balance of the entire organic EL device. Themain factors that control the carrier balance are carrier transportingcapability of each of the organic layers and carrier injectingcapability in the interfacial region of separate organic layers. In theorganic EL devices having the co-host combinations of the presentdisclosure, the co-host materials provide an improved charge carrierbalance of the entire organic EL device by putting two of positive holetransportability materials and electronic transportability materialstogether. The provision of such co-host materials reduces deteriorationby the carrier invasion to the adjacent layer.

For example, the inventors have found that the emitter host materialsrepresented by the formulas (1A) and (2A) in the present disclosure notonly function well as a single host in an emitter layer but also ascohosts. This is because the organic compounds represented by theformulas (1A) and (2A) have a biscarbazole skeleton having an excellenthole transporting capability as well as a heterocyclic skeleton havingan excellent electron transporting capability. Providing these twocompounds as cohosts in the emitter layer, the carrier injectingcapability to neighboring layers in the emitting layer (recombinationregion) is balanced.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic drawing of an exemplary arrangement for an OLEDaccording to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

The OLEDs of the present invention may comprise a plurality of layerslocated between an anode and a cathode. Representative OLEDs accordingto the invention include, but are not limited to, structures havingconstituent layers as described below:

-   -   (1) anode/light emitting layer/cathode;    -   (2) anode/hole injecting layer/light emitting layer/cathode:    -   (3) anode/light emitting layer/electron injecting•transporting        layer/cathode;    -   (4) anode/hole injecting layer/light emitting layer/electron        injecting•transporting layer/cathode;    -   (5) anode/organic semiconductor layer/light emitting        layer/cathode;    -   (6) anode/organic semiconductor layer/electron blocking        layer/light emitting layer/cathode;    -   (7) anode/organic semiconductor layer/light emitting        layer/adhesion improving layer/cathode;    -   (8) anode/hole injecting•transporting layer/light emitting        layer/electron injecting•transporting layer/cathode;    -   (9) anode/insulating layer/light emitting layer/insulating        layer/cathode;    -   (10) anode/inorganic semiconductor layer/insulating layer/light        emitting layer/insulating layer/cathode;    -   (11) anode/organic semiconductor layer/insulating layer/light        emitting layer/insulating layer/cathode;    -   (12) anode/insulating layer/hole injecting•transporting        layer/light emitting layer/insulating layer/cathode; and    -   (13) anode/insulating layer/hole injecting•transporting        layer/light emitting layer/electron injecting•transporting        layer/cathode.

Among the OLED constituent structures described above, constituentstructure number (8) is a preferred structure, but the present inventionis not limited to these disclosed constituent structures.

FIG. 1 shows an OLED 1 according to an embodiment. The OLED 1 comprisesa transparent substrate 2, an anode 3, a cathode 4 and a plurality oforganic thin film layers 10 disposed between the anode 3 and the cathode4. At least one of the plurality of organic thin film layers 10 is aphosphorescence emitting layer 5 comprising one or more phosphorescenthost material and a phosphorescent dopant material.

The plurality of organic thin film layers 10 can include other layerssuch as a hole injecting•transporting layer 6 and the like between thephosphorescence emitting layer 5 and the anode 3. The plurality oforganic thin film layers 10 can also include layers such as an electroninjecting•transporting layer 7 and the like between the phosphorescenceemitting layer 5 and the cathode 4.

Further, there may be provided respectively an electron blocking layerdisposed between the anode 3 and the phosphorescence emitting layer 5,and a hole blocking layer disposed between the cathode 4 and thephosphorescence emitting layer 5. This makes it possible to containelectrons and holes in the phosphorescence emitting layer 5 to enhancethe production rate of excitons in the phosphorescence emitting layer 5.

In the present disclosure, the term “phosphorescent host” is used torefer to a host material that functions as a phosphorescent host whencombined with a phosphorescent dopant and should not be limited to aclassification of the host material based solely on molecular structure.

Thus, a phosphorescent host means a material constituting thephosphorescence emitting layer containing a phosphorescent dopant anddoes not mean a material which can be used only for a host of aphosphorescent material. A phosphorescence emitting layer is alsoreferred to herein as a light emitting layer.

In the present specification, “a hole injecting•transporting layer”means at least either one of a hole injecting layer and a holetransporting layer, and “an electron injecting•transporting layer” meansat least either one of an electron injecting layer and an electrontransporting layer.

[Substrate]

The OLED of the present disclosure may be prepared on a substrate. Thesubstrate referred to in this case is a substrate for supporting theOLED, and it is preferably a flat substrate in which light in thevisible region of about 400 to about 700 nm has a transmittance of atleast about 50%.

The substrate may include a glass plate, a polymer plate and the like.In particular, the glass plate may include soda lime glass,barium•strontium-containing glass, lead glass, aluminosilicate glass,borosilicate glass, barium borosilicate glass, quartz and the like. Thepolymer plate may include polycarbonate, acryl, polyethyleneterephthalate, polyether sulfide, polysulfone and the like.

[Anode and Cathode]

An anode in the OLED of the present disclosure assumes the role ofinjecting a hole into the hole injecting layer, the hole transportinglayer or the light emitting layer. Typically the anode has a workfunction of 4.5 eV or more.

Specific examples of a material suitable for use as the anode includeindium tin oxide alloy (ITO), tin oxide (NESA glass), indium zinc oxide,gold, silver, platinum, copper and the like. The anode can be preparedby forming a thin film from electrode substances, such as thosediscussed above, by a method such as a vapor deposition method, asputtering method and the like.

When light is emitted from the light emitting layer, the transmittanceof light in the visible light region in the anode is preferably largerthan 10%. The sheet resistance of the anode is preferably severalhundred Ω/square or less. The film thickness of the anode is selected,depending on the material, and is typically in the range of from about10 nm to about 1 μm, and preferably from about 10 nm to about 200 nm.

The cathode comprises preferably a material having a small work functionfor the purpose of injecting an electron into the electron injectinglayer, the electron transporting layer or the light emitting layer.Materials suitable for use as the cathode include, but are not limitedto indium, aluminum, magnesium, magnesium-indium alloys,magnesium-aluminum alloys, aluminum-lithium alloys,aluminum-scandium-lithium alloys, magnesium-silver alloys and the like.For transparent or top-emitting devices, a TOLED cathode such asdisclosed in U.S. Pat. No. 6,548,956 is preferred.

The cathode can be prepared, as is the case with the anode, by forming athin film by a method such as a vapor deposition method, a sputteringmethod and the like. Further, an embodiment in which light emission istaken out from a cathode side can be employed as well.

[Light Emitting Layer According to First Embodiment]

The light emitting layer in the OLED of the present disclosure may becapable of carrying out the following functions singly or incombination:

-   -   (1) injecting function: a function in which a hole can be        injected from an anode or a hole injecting layer in applying an        electric field and in which an electron can be injected from a        cathode or an electron injecting layer;    -   (2) transporting function: a function in which a charge        (electron and hole) injected may be transferred by virtue of a        force of an electric field; and    -   (3) light emitting function: a function in which a region for        recombination of an electron and a hole may be provided, and        which results in the emission of light.

A difference may be present between ease of injection of a hole and easeof injection of an electron, and a difference may be present in thetransporting ability shown by the mobilities of a hole and an electron.

Known methods including, for example, vapor deposition, spin coating,Langmuir Blodgett methods and the like can be used to prepare the lightemitting layer. The light emitting layer is preferably a molecularlydeposited film. In this regard, the term “molecularly deposited film”means a thin film formed by depositing a compound from the gas phase anda film formed by solidifying a material compound in a solution state ora liquid phase state, and usually the above-referenced molecular depositfilm can be distinguished from a thin film (molecular accumulation film)formed by an LB method by a difference in an aggregation structure and ahigher order structure and a functional difference originating in it.

In preferred embodiments, the film thickness of the light emitting layeris preferably from about 5 to about 50 nm, more preferably from about 7to about 50 nm and most preferably from about 10 to about 50 nm. If thefilm thickness is less than 5 nm, it is likely to be difficult to formthe light emitting layer and control the chromaticity. On the otherhand, if it exceeds about 50 nm, the operating voltage is likely to goup.

[Biscarbazole Host Material]

The at least one of the plurality of organic thin film layers 10 in theOLED according to an embodiment of the present disclosure is the lightemitting layer comprising novel combination of a biscarbazole derivativecompound as a host material in the light emitting region of the deviceand an organometallic phostphorescent material as a dopant in the lightemitting region. The host material is a biscarbazole derivative compoundrepresented by a formula (1A) or (2A) below:

where A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 carbon atoms forming a ring;

A₂ represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, or substituted or unsubstitutednitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms;

X₁ and X₂ each independently represents substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3; and

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different.

According to another aspect of the present disclosure, in the devices ofthe present embodiment, the A₁ in the host compound can represent asubstituted or unsubstituted benzofuranyl group, a substituted orunsubstituted dibenzofuranyl group, a substituted or unsubstitutedbenzothiophenyl group, a substituted or unsubstituted dibenzothiophenylgroup, a substituted or unsubstituted benzonaphthofuranyl group, or asubstituted or unsubstituted benzonaphthothiophenyl group.

[Phosphorescent Material]

The phosphorescent material is an organometallic compound having asubstituted chemical structure represented by the following formula(4A):

where each R is independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl, heteroaryl,substituted aryl, substituted heteroaryl or a heterocyclic group;

M is a platinum group metal;

Ar′, Ar″, Ar′″ and Ar″″ each independently represent a substituted orunsubstituted aryl or heteroaryl substituent on the phenylpyridineligand;

a is 0 or 1;b is 0 or 1;c is 0 or 1;d is 0 or 1;m is 1 or 2;n is 1 or 2;m+n is the maximum number of ligands that can be coordinated to M, andwherein at least one of a, b, c, and d is 1 and when at least one of aand b is 1 and at least one of b and c is 1, at least one of Ar′ and Ar″is different from at least one of Ar′″ and Ar″″.

In another embodiment, M can be a platinum group metal atom andpreferably, M is a metal atom selected from iridium (Ir), Osmium (Os),and platinum (Pt).

According to another embodiment, the phosphorescent material can be acompound represented by the following formula (4B):

In the OLEDs of the above two embodiments, the host material can be abiscarbazole derivative compound represented by a formula (1C) or (2C)below:

[EIL/ETL]

The electron injecting layer or the electron transporting layer, whichaids injection of the electrons into the emitting layer, has a largeelectron mobility. The electron injecting layer is provided foradjusting energy level, by which, for instance, sudden changes of theenergy level can be reduced.

The organic EL device according to this embodiment preferably includesthe electron injecting layer between the emitting layer and the cathode,and the electron injecting layer preferably contains anitrogen-containing cyclic derivative as the main component. Theelectron injecting layer may serve as the electron transporting layer.It should be noted that “as the main component” means that thenitrogen-containing cyclic derivative is contained in the electroninjecting layer at a content of 50 mass % or more.

A preferable example of an electron transporting material for formingthe electron injecting layer is an aromatic heterocyclic compound havingin the molecule at least one heteroatom. Particularly, anitrogen-containing cyclic derivative is preferable. Thenitrogen-containing cyclic derivative is preferably an aromatic ringhaving a nitrogen-containing six-membered or five-membered ringskeleton, or a fused aromatic cyclic compound having anitrogen-containing six-membered or five-membered ring skeleton.

The nitrogen-containing cyclic derivative is preferably exemplified by anitrogen-containing cyclic metal chelate complex represented by thefollowing formula (E1).

R² to R⁷ in the formula (E1) each independently represent a hydrogenatom, a halogen atom, an oxy group, an amino group, a hydrocarbon grouphaving 1 to 40 carbon atoms, an alkoxy group, an aryloxy group, analkoxycarbonyl group, or an aromatic heterocyclic group. These groupsmay be substituted or unsubstituted.

Examples of the halogen atom include fluorine, chlorine, bromine, andiodine. In addition, examples of the substituted or unsubstituted aminogroup include an alkylamino group, an arylamino group, and anaralkylamino group.

The alkoxycarbonyl group is represented by —COOY′. Examples of Y′ arethe same as the examples of the alkyl group. The alkylamino group andthe aralkylamino group are represented by —NQ¹Q². Examples for each ofQ¹ and Q² are the same as the examples described in relation to thealkyl group and the aralkyl group, and preferred examples for each of Q¹and Q² are also the same as those described in relation to the alkylgroup and the aralkyl group. Either one of Q¹ and Q² may be a hydrogenatom.

The arylamino group is represented by —NAr¹Ar². Examples for each of Ar¹and Ar² are the same as the examples described in relation to thenon-fused aromatic hydrocarbon group and the fused aromatic hydrocarbongroup. Either one of Ar¹ and Ar² may be a hydrogen atom.

M in the formula (E1) represents aluminum (Al), gallium (Ga) or indium(In), among which In is preferable.

L in the formula (E1) represents a group represented by a formula (A′)or (A″) below.

In the formula (A′), R⁸ to R¹² each independently represent a hydrogenatom or a substituted or unsubstituted hydrocarbon group having 1 to 40carbon atoms. Adjacent groups may form a cyclic structure. In theformula (A″), R¹³ to R²⁷ each independently represent a hydrogen atom ora substituted or unsubstituted hydrocarbon group having 1 to 40 carbonatoms. Adjacent groups may form a cyclic structure.

Examples of the hydrocarbon group having 1 to 40 carbon atomsrepresented by each of R⁸ to R¹² and R¹³ to R²⁷ in the formulas (A′) and(A″) are the same as those of R² to R⁷ in the formula (E1).

Examples of a divalent group formed when an adjacent set of R⁸ to R¹²and R¹³ to R²⁷ forms a cyclic structure are a tetramethylene group, apentamethylene group, a hexamethylene group, a diphenylmethane-2,2′-diylgroup, a diphenylethane-3,3′-diyl group, a diphenylpropane-4,4′-diylgroup and the like.

As an electron transporting compound for the electron injecting layer orthe electron transporting layer, 8-hydroxyquinoline or a metal complexof its derivative, an oxadiazole derivative and a nitrogen-containingheterocyclic derivative are preferable. A specific example of the8-hydroxyquinoline or the metal complex of its derivative is a metalchelate oxinoid compound containing a chelate of oxine (typically8-quinolinol or 8-hydroxyquinoline). For instance,tris(8-quinolinol)aluminum can be used. Examples of the oxadiazolederivative are represented by the following formulas:

In the formulas above, Ar¹⁷, Ar¹⁸, Ar¹⁹, Ar²¹, Ar²² and Ar²⁵ eachrepresent a substituted or unsubstituted aromatic hydrocarbon group orfused aromatic hydrocarbon group having 6 to 40 ring carbon atoms. Ar¹⁷,Ar¹⁹ and Ar²² may be the same as or different from Ar¹⁸, Ar²¹ and Ar²⁵respectively. Examples of the aromatic hydrocarbon group or fusedaromatic hydrocarbon group having 6 to 40 ring carbon atoms are a phenylgroup, biphenyl group, anthranil group, perylenyl group and pyrenylgroup. Examples of the substituent therefor are an alkyl group having 1to 10 carbon atoms, alkoxy group having 1 to 10 carbon atoms and cyanogroup.

Ar²⁰, Ar.²³ and Ar²⁴ each represent a substituted or, unsubstituteddivalent aromatic hydrocarbon group or fused aromatic hydrocarbon grouphaving 6 to 40 ring carbon atoms. Ar²³ and Ar²⁴ may be mutually the sameor different. Examples of the divalent aromatic hydrocarbon group orfused aromatic hydrocarbon group having 6 to 40 ring carbon atoms are aphenylene group, naphthylene group, biphenylene group, anthranylenegroup, perylenylene group and pyrenylene group. Examples of thesubstituent therefor are an alkyl group having 1 to 10 carbon atoms,alkoxy group having 1 to 10 carbon atoms and cyano group.

Preferably, such electron transport compound can be favorably formedinto a thin film(s). Some examples of the electron transportingcompounds are as follows.

An example of the nitrogen-containing heterocyclic derivative as theelectron transporting compound is a nitrogen-containing compound that isnot a metal complex, the derivative being formed of an organic compoundrepresented by one of the following general formulae. Examples of thenitrogen-containing heterocyclic derivative are a five-membered ring orsix-membered ring derivative having a skeleton represented by thefollowing formula (A) and a derivative having a structure represented bythe following formula (B).

In the formula (B) above, X represents a carbon atom or a nitrogen atom.Z₁ and Z₂ each independently represent a group of atoms capable offorming a nitrogen-containing heterocycle.

Preferably, the nitrogen-containing heterocyclic derivative is anorganic compound having a nitrogen-containing aromatic polycyclic grouphaving a five-membered ring or six-membered ring. When thenitrogen-containing heterocyclic derivative includes suchnitrogen-containing aromatic polycyclic series having plural nitrogenatoms, the nitrogen-containing heterocyclic derivative may be anitrogen-containing aromatic polycyclic organic compound having askeleton formed by a combination of the skeletons respectivelyrepresented by the formulas (A) and (B), or by a combination of theskeletons respectively represented by the formulas (A) and (C).

A nitrogen-containing group of the nitrogen-containing aromaticpolycyclic organic compound is selected from nitrogen-containingheterocyclic groups respectively represented by the following generalformulas:

where, R represents an aromatic hydrocarbon group or fused aromatichydrocarbon group having 6 to 40 ring carbon atoms, an aromaticheterocyclic group or fused aromatic heterocyclic group having 2 to 40ring carbon atoms, an alkyl group having 1 to 20 carbon atoms or alkoxygroup having 1 to 20 carbon atoms, and n represents an integer in arange of 0 to 5. When n is an integer of 2 or more, plural R may bemutually the same or different.

An example of a preferable specific compound is a nitrogen-containingheterocyclic derivative represented by the following formula:

HAr-L¹-Ar¹—Ar²

Where, HAr represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 40 ring carbon atoms, L¹ represents asingle bond, substituted or unsubstituted aromatic hydrocarbon group orfused aromatic hydrocarbon group having 6 to 40 ring carbon atoms, orsubstituted or unsubstituted aromatic heterocyclic group or fusedaromatic heterocyclic group having 2 to 40 ring carbon atoms, Ar¹represents a substituted or unsubstituted divalent aromatic hydrocarbongroup having 6 to 40 ring carbon atoms; and Ar² represents a substitutedor unsubstituted aromatic hydrocarbon group or fused aromatichydrocarbon group having 6 to 40 ring carbon atoms, or substituted orunsubstituted aromatic heterocyclic group or fused aromatic heterocyclicgroup having 2 to 40 ring carbon atoms.

Examples of HAr can be selected from the following group:

Examples of L¹ can be selected from the following group:

Examples of Ar¹ can be selected from the following group:

where, R¹ to R¹⁴ each independently represent a hydrogen atom, halogenatom, alkyl group having 1 to 20 carbon atoms, alkoxy group having 1 to20 carbon atoms, aryloxy group having 6 to 40 ring carbon atoms,substituted or unsubstituted aromatic hydrocarbon group or fusedaromatic hydrocarbon group having 6 to 40 ring carbon atoms, or aromaticheterocyclic group or fused aromatic heterocyclic group having 2 to 40ring carbon atoms; and Ar³ represents aromatic hydrocarbon group orfused aromatic hydrocarbon group having 6 to 40 ring carbon atoms, oraromatic heterocyclic group or fused aromatic heterocyclic group having2 to 40 ring carbon atoms.

All of R¹ to R⁸ of a nitrogen-containing heterocyclic. derivative may behydrogen atoms.

Examples of Ar² can be selected from the following group:

In addition to the above examples, the following nitrogen-containingaromatic polycyclic organic compound (see JP-A-9-3448) can be favorablyused as the electron transporting compound.

where, R₁ to R₄ each independently represent a hydrogen atom,substituted or unsubstituted aliphatic group, substituted orunsubstituted alicyclic group, substituted or unsubstituted carbocyclicaromatic cyclic group or substituted or unsubstituted heterocyclicgroup; and X₁ and X₂ each independently represent an oxygen atom, sulfuratom or dicyanomethylene group.

Additional examples of compounds that can be used as electrontransporting material can be found in JP-A-2000-173774.

The electron injecting layer preferably contains an inorganic compoundsuch as an insulator or a semiconductor in addition to thenitrogen-containing cyclic derivative. Such an insulator or asemiconductor, when contained in the electron injecting layer, caneffectively prevent a current leak, thereby enhancing electroncapability of the electron injecting layer.

As the insulator, it is preferable to use at least one metal compoundselected from the group consisting of an alkali metal chalcogenide, analkali earth metal chalcogenide, a halogenide of alkali metal and ahalogenide of alkali earth metal. By forming the electron injectinglayer from the alkali metal chalcogenide or the like, the electroninjecting capability can preferably be further enhanced. Specifically,preferred examples of the alkali metal chalcogenide are Li₂O, K₂O, Na₂S,Na₂Se and Na₂O, while preferable example of the alkali earth metalchalcogenide are CaO, BaO, SrO, BeO, BaS and CaSe. Preferred examples ofthe halogenide of the alkali metal are LiF, NaF, KF, LiCl, KCl and NaCl.Preferred examples of the halogenide of the alkali earth metal arefluorides such as CaF₂, BaF₂, SrF₂, MgF₂ and BeF₂, and halogenides otherthan the fluoride.

Examples of the semiconductor are one of or a combination of two or moreof an oxide, a nitride or an oxidized nitride containing at least oneelement selected from Ba, Ca, Sr, Yb, Al, Ga, In, Li, Na, Cd, Mg, Si,Ta, Sb and Zn. An inorganic compound for forming the electron injectinglayer is preferably a microcrystalline or amorphous semiconductor film.When the electron injecting layer is formed of such insulator film, moreuniform thin film can be formed, thereby reducing pixel defects such asa dark spot. Examples of such an inorganic compound are theabove-described alkali metal chalcogenide, alkali earth metalchalcogenide, halogenide of the alkali metal and halogenide of thealkali earth metal.

When the electron injecting layer contains such an insulator or such asemiconductor, a thickness thereof is preferably in a range ofapproximately 0.1 nm to 15 nm. The electron injecting layer in thisexemplary embodiment may preferably contain the above-describedreduction-causing dopant.

[HIL/HTL]

The hole injecting layer or the hole transporting layer (including thehole injecting/transporting layer) may contain an aromatic aminecompound such as an aromatic amine derivative represented by thefollowing general formula (I).

where, Ar¹ to Ar⁴ each represent a substituted or unsubstituted aromatichydrocarbon group or fused aromatic hydrocarbon group having 6 to 50ring carbon atoms, substituted or unsubstituted aromatic heterocyclicgroup or fused aromatic heterocyclic group having 2 to 40 ring carbonatoms, or a group formed by combining the aromatic hydrocarbon group orthe fused aromatic hydrocarbon group with the aromatic heterocyclicgroup or fused aromatic heterocyclic group.

Some examples of the compound represented by the general formula (I) canbe found, for example, in United States Patent Application PublicationNo. US 2011/0278555 A1, the disclosures of which is incorporated hereinby reference. However, the compound represented by the general formula(I) is not limited thereto.

Aromatic amine represented by the following formula (II) can also beused for forming the hole injecting layer or the hole transportinglayer.

where, Ar¹ to Ar³ each represent the same as Ar¹ to Ar⁴ of the formula(I) above. Some examples of the compound represented by the generalformula (II) can be found, for example, in United States PatentApplication Publication No. US 2011/0278555 A1, the disclosures of whichis incorporated herein by reference. However, the compound representedby the general formula (II) is not limited thereto.

A method of forming each of the layers in the organic EL device of thevarious embodiments described herein is not particularly limited. Aconventionally-known methods such as vacuum deposition or spin coatingmay be employed for forming the layers. The organic thin-film layercontaining the compound represented by the formula (1A) or (1B), whichis used in the organic EL device according to this exemplary embodiment,may be formed by a conventional coating method such as vacuumdeposition, molecular beam epitaxy (MBE method) and coating methodsusing a solution such as a dipping, spin coating, casting, bar coating,and roll coating.

Although the thickness of each organic layer of the organic EL deviceaccording to this exemplary embodiment is not particularly limited, thethickness is generally preferably in a range of several nanometers to 1μm because an excessively-thinned film likely entails defects such as apin hole while an excessively-thickened film requires high voltage to beapplied and deteriorates efficiency.

In an OLED embodiment according to the present disclosure, a pluralityof organic thin film layers provided between a cathode and an anode; theplurality of organic thin film layers comprise at least onephosphorescence emitting layer comprising at least one phosphorescentmaterial and at least one biscarbazole derivative host material asdescribed below.

As described above, a phosphorescence emitting layer having highefficiency and long lifetime can be prepared according to the teachingsof the present invention, especially a high stability at high operatingtemperatures.

In this regard, an excited triplet energy gap Eg(T) of the materialconstituting the OLED of the present disclosure may be prescribed basedon its phosphorescence emission spectrum, and it is given as an examplein the present disclosure that the energy gap may be prescribed, as iscommonly used, in the following manner.

The respective materials are dissolved in an EPA solvent (diethylether:isopentane:ethanol=5:5:2 in terms of a volume ratio) in aconcentration of 10 μmol/L to prepare a sample for measuringphosphorescence. This phosphorescence measuring sample is placed in aquartz cell and cooled to 77 K, and is subsequently irradiated withexciting light to measure the wavelength of a phosphorescence emitted.

A tangent line is drawn based on the increase of phosphorescenceemission spectrum thus obtained at the short wavelength side, and thewavelength value of the intersection point of the above tangent line andthe base line is converted to an energy value, which is set as anexcited triplet energy gap Eg(T). A commercially available measuringequipment F-4500 (manufactured by Hitachi, Ltd.) can be used for themeasurement.

However, a value which can be defined as the triplet energy gap can beused without depending on the above procedure as long as it does notdeviate from the scope of the present invention.

According to another embodiment, an organic EL device comprises acathode, an anode, and a plurality of organic thin-film layers providedbetween the cathode and the anode and at least one of the plurality oforganic thin-film layers comprise an emitting layer comprising a pair ofco-host materials and a phosphorescent material providingphosphorescence. The first host material of the pair of co-hostmaterials is a biscarbazole derivative compound represented by a formula(1A) below:

where A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms;

A₂ represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, or substituted or unsubstitutednitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms;

X₁ and X₂ each independently represents substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3;

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different. Thesecond host material of the pair of co-host materials is a biscarbazolederivative compound represented by a formula (2A) below:

where X₂ represents a single bond, substituted or unsubstituted aromatichydrocarbon group having 6 to 30 ring carbon atoms, substituted orunsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3; and

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different.

In the organic EL device according to another aspect of the presentdisclosure, the A₁ in the first host compound and/or the second hostcompound can represent a substituted or unsubstituted benzofuranylgroup, a substituted or unsubstituted dibenzofuranyl group, asubstituted or unsubstituted benzothiophenyl group, a substituted orunsubstituted dibenzothiophenyl group, a substituted or unsubstitutedbenzonaphthofuranyl group, or a substituted or unsubstitutedbenzonaphthothiophenyl group.

The phosphorescent material in the organic EL device of the presentembodiment can be an organometallic compound having a substitutedchemical structure represented by the following formula (4A):

where each R is independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl, heteroaryl,substituted aryl, substituted heteroaryl or a heterocyclic group;

M is a platinum group metal atom;

Ar′, Ar″, Ar′″ and Ar″″ each independently represent a substituted orunsubstituted aryl or heteroaryl substituent on the phenylpyridineligand;

a is 0 or 1;b is 0 or 1;c is 0 or 1;d is 0 or 1;m is 1 or 2;n is 1 or 2;m+n is the maximum number of ligands that can be coordinated to M, andwherein at least one of a, b, c, and d is 1 and when at least one of aand b is 1 and at least one of b and c is 1, at least one of Ar′ and Ar″is different from at least one of Ar′″ and Ar″″.

In the devices of the present embodiment, M can be a metal atom selectedfrom iridium (Ir), Osmium (Os), and platinum (Pt).

In the organic EL device of the present embodiment, the phosphorescentmaterial can be an organometallic compound represented by the followingformula (4B) below:

According to another aspect of the present disclosure, in the devices ofthe present embodiment, the A₁ in the first host compound and/or thesecond host compound can represent a substituted or unsubstitutedbenzofuranyl group, a substituted or unsubstituted dibenzofuranyl group,a substituted or unsubstituted benzothiophenyl group, a substituted orunsubstituted dibenzothiophenyl group, a substituted or unsubstitutedbenzonaphthofuranyl group, or a substituted or unsubstitutedbenzonaphthothiophenyl group.

In the devices of the present embodiment, the first host material can bea biscarbazole derivative compound represented by a formula (1C) below:

In the devices of the present embodiment, the second host material canbe a biscarbazole derivative compound represented by a formula (2C)below:

According to another embodiment, an organic EL device comprises acathode, an anode, and a plurality of organic thin-film layers providedbetween the cathode and the anode. At least one of the organic thin-filmlayers is an emitting layer comprising a pair of co-host materials and aphosphorescent material providing phosphorescence. The first hostmaterial of the pair of co-host materials is a biscarbazole derivativecompound represented by a formula (1A) below:

where A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms;

A₂ represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, or substituted or unsubstitutednitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms;

X₁ and X₂ each are independently represents substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms;

Y₁ to Y₄ independently represent a hydrogen atom, fluorine atom, cyanogroup, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms, substituted or unsubstituted alkoxy group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkyl group having 1 to 20carbon atoms, substituted or unsubstituted haloalkoxy group having 1 to20 carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms;

adjacent ones of Y₁ to Y₄ are allowed to be bonded to each other to forma ring structure;

p and q represent an integer of 1 to 4; r and s represent an integer of1 to 3;

when p and q are an integer of 2 to 4 and r and s are an integer of 2 to3, a plurality of Y₁ to Y₄ are allowed to be the same or different. Thesecond host material of the pair of co-host materials is a biscarbazolederivative compound represented by a formula (3A) below:

where G is substituted or unsubstituted aryl group having 6 to 40 carbonatoms, or represented by a formula 3(b) below:

where in formula 3(b), * represents link with L³;in formula (3A), X₁ is sulfur atom or represents N—R⁹;in formula 3(b), X₂ is sulfur atom or represents N—R¹⁰;

R¹ to R⁸ each represent independently an alkyl group having 1 to 5carbon atoms, substituted or unsubstituted cycloalkyl group having 3 to6 carbon atoms, substituted or unsubstituted alcoxy group having 1 to 5carbon atoms, substituted or unsubstituted cycloalkoxy group having 3 to6 carbon atoms, substituted or unsubstituted aryl group having 6 to 18carbon atoms, substituted or unsubstituted aryloxy group having 6 to 18carbon atoms, substituted or unsubstituted heteroaryl group having 5 to18 carbon atoms, substituted by alkyl group having 1 to 5 carbon atomsor unsubstituted amino group, substituted by alkyl group having 1 to 6carbon atoms or unsubstituted silyl group, a fluoro group or a cyanogroup. R¹ to R⁸ being optionally bonded to each other to form a ringstructure;

when G or R¹ to R⁸ have a substituent, R each represent independently analkyl group having 1 to 5 carbon atoms, cycloalkyl group having 3 to 6carbon atoms, alcoxy group having 1 to 4 carbon atoms, cycloalkoxy grouphaving 3 to 6 carbon atoms, aryl group having 6 to 18 carbon atoms,aryloxy group having 6 to 18 carbon atoms, heteroaryl group having 5 to18 carbon atoms, substituted by alkyl group having 1 to 5 carbon atomsor unsubstituted amino group, substituted by alkyl group having 1 to 6carbon atoms or unsubstituted silyl group, a fluoro group or a cyanogroup;

a, d and f each represent independently an integer of any of 0 to 4, andb, c and e each represent independently an integer of any of 0 to 3; asum of a to f is 4 or less;

R⁹ to R¹⁰ each represent independently an alkyl group having 1 to 5carbon atoms, phenyl group, toluyl group, dimethyl phenyl group,trimethyl phenyl group, biphenyl group, dibenzofuranyl group ordibenzothiophenyl group;

g represents an integer of any of 0 to 3, and h represents an integer ofany of 0 to 4; a sum of g and h is 4 or less;

provided that when X¹ and X² are nitrogen, and R⁹ is phenyl group, R¹⁰is not phenyl group;

L¹ represents a single bond, a divalent linkage group containing N, adivalent linkage group containing O, a divalent linkage group containingSi, a divalent linkage group containing P, a divalent linkage groupcontaining S, an alkylene group having 1 to 5 carbon atoms,cycloalkylene group having 3 to 6 carbon atoms, arylene group having 6to 18 carbon atoms or heteroarylene group having 5 to 18 carbon atoms;

L² and L³ each represent independently a single bond, an alkylene grouphaving 1 to 5 carbon atoms, cycloalkylene group having 3 to 6 carbonatoms, arylene group having 6 to 18 carbon atoms or heteroarylene grouphaving 5 to 18 carbon atoms;

L¹ to L³ may be further substituted with the substituent R describedabove; provided that when L¹ is an arylene group or a heteroarylenegroup, a and d each represent independently an integer of any of 1 to 4.

According to another aspect of the present disclosure, in the devices ofthe present embodiment, the A₁ in the first host compound can representa substituted or unsubstituted benzofuranyl group, a substituted orunsubstituted dibenzofuranyl group, a substituted or unsubstitutedbenzothiophenyl group, a substituted or unsubstituted dibenzothiophenylgroup, a substituted or unsubstituted benzonaphthofuranyl group, or asubstituted or unsubstituted benzonaphthothiophenyl group.

In the device of the present embodiment, the phosphorescent material canbe an organometallic compound having a substituted chemical structurerepresented by the following formula (4A):

where each R is independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, CF_(2n+1), trifluorovinyl,CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl, heteroaryl, substituted aryl,substituted heteroaryl or a heterocyclic group;

M is a platinum group metal atom;

Ar′, Ar″, Ar′″ and Ar″″ each independently represent a substituted orunsubstituted aryl or heteroaryl substituent on the phenylpyridineligand;

a is 0 or 1;b is 0 or 1;c is 0 or 1;d is 0 or 1;m is 1 or 2;n is 1 or 2;m+n is the maximum number of ligands that can be coordinated to M, andwhere at least one of a, b, c, and d is 1 and when at least one of a andb is 1 and at least one of b and c is 1, at least one of Ar′ and A′ isdifferent from at least one of Ar′″ and Ar″″.

According to another aspect of the present disclosure, M in formula (4A)can be a metal atom selected from iridium (Ir), Osmium (Os), andplatinum (Pt).

In the devices of the present embodiment, the phosphorescent materialcan be an organometallic compound represented by the following formula(4B) below:

In the devices of the present embodiment, the first host material can bea biscarbazole derivative compound represented by a formula (1C) below:

In the device of the present embodiment, the second host material can bea biscarbazole derivative compound represented by a formula (3B) below:

According to another aspect of the present disclosure, the scope of theinvention described herein includes a lighting apparatus and/or displayapparatus that incorporates one or more of the various embodiments ofthe organic electroluminescence devices described herein. Some examplesof such display apparatus are television screens, computer displayscreens, mobile phone display screens, billboard screens, etc.

In the biscarbazole derivative disclosed herein, when Y₁ to Y₄ arebonded to each other to form a ring structure, the ring structure isexemplified by structures represented by the following formulas:

Moreover, A₁ in the formula (1A) or (2A) is preferably selected from thegroup consisting of a substituted or unsubstituted pyridine ring,substituted or unsubstituted pyrimidine ring and substituted orunsubstituted triazine ring, more preferably selected from a substitutedor unsubstituted pyrimidine ring or substituted or unsubstitutedtriazine ring, and further preferably a substituted or unsubstitutedpyrimidine ring.

Moreover, according to the above aspect, A₁ in the formula (1A) or (2A)is preferably a substituted or unsubstituted quinazoline ring.

In the formula (1A) or (2A) X₁ is preferably a single bond orsubstituted or unsubstituted divalent aromatic hydrocarbon group having6 to 30 ring carbon atoms, particularly preferably a benzene ring.

In the formula (1A) or (2A) when X₁ is a substituted or unsubstitutedbenzene ring, A₁ and the carbazolyl group, which are bonded to X₁, arepreferably in meta positions or para positions. Particularly preferably,X₁ is unsubstituted para-phenylene.

In the formula (1A) or (2A), the pyridine ring, pyrimidine ring andtriazine ring are more preferably represented by the following formulas.In the formulas, Y and Y′ represent a substituent. Examples of thesubstituent are the same groups as those represented by Y₁ to Y₄ asdescribed above. Y and Y′ may be the same or different. Preferredexamples thereof are the substituted or unsubstituted aromatichydrocarbon group or fused aromatic hydrocarbon group having 6 to 30ring carbon atoms, and the substituted or unsubstituted aromaticheterocyclic group or fused aromatic heterocyclic group having 2 to 30ring carbon atoms. In the following formulas, * represents a bondingposition to X₁ or X₂.

In the formula (1A) or (2A), the quinazoline ring is represented by thefollowing formula. Y represents a substituent. u represents an integerof 1 to 5. When u is an integer of 2 to 5, a plurality of Y may be thesame or different. As the substituent Y, the same groups as those forthe above Y₁ to Y₄ are usable, among which preferred examples thereofare the substituted or unsubstituted aromatic hydrocarbon group or fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, and thesubstituted or unsubstituted aromatic heterocyclic group or fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms. Also inthe following formulas, * represents a bonding position to X₁ or X₂.

In the formulae (1A) to (2A), the alkyl group, alkoxy group, haloalkylgroup, haloalkoxy group and alkylsilyl group, which are represented byY₁ to Y₅, may be linear, branched or cyclic.

In the formulae (1A) to (2B), examples of the alkyl group having 1 to 20carbon atoms are a methyl group, ethyl group, propyl group, isopropylgroup, n-butyl group, s-butyl group, isobutyl group, t-butyl group,n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonylgroup, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecylgroup, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group,n-heptadecyl group, n-octadecyl group, neo-pentyl group, 1-methylpentylgroup, 2-methylpentyl group, 1-pentylhexyl group, 1-butylpentyl group,1-heptyloctyl group, 3-methylpentyl group, cyclopentyl group, cyclohexylgroup, cycloheptyl group, cyclooctyl group and 3,5-tetramethylcyclohexylgroup. An alkyl group having 1 to 10 carbon atoms is preferable,examples of which are a methyl group, ethyl group, propyl group,isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butylgroup, cyclopentyl group, cyclohexyl group and cycloheptyl group.

As the alkoxy group having 1 to 20 carbon atoms, an alkoxy group having1 to 6 carbon atoms is preferable and specific examples thereof are amethoxy group, ethoxy group, propoxy group, butoxy group, pentyloxygroup, and hexyloxy group.

The haloalkyl group having 1 to 20 carbon atoms is exemplified by ahaloalkyl group provided by substituting the alkyl group having 1 to 20carbon atoms with one or more halogen atoms. Preferred one of thehalogen atoms is fluorine. The haloalkyl group is exemplified by atrifluoromethyl group and a 2,2,2-trifluoroethyl group.

The haloalkoxy group having 1 to 20 carbon atoms is exemplified by ahaloalkoxy group provided by substituting the alkoxy group having 1 to20 carbon atoms with one or more halogen atoms. Preferred one of thehalogen atoms is fluorine.

Examples of the alkylsilyl group having 1 to 10 carbon atoms are atrimethylsilyl group, triethylsilyl group, tributylsilyl group,dimethylethylsilyl group, dimethylisopropylsilyl group,dimethylpropylsilyl group, dimethylbutylsilyl group,dimethyl-tertiary-butylsilyl group and diethylisopropylsilyl group.

Examples of the arylsilyl group having 6 to 30 carbon atoms are aphenyldimethylsilyl group, diphenylmethylsilyl group,diphenyl-tertiary-butylsilyl group and triphenylsilyl group.

Examples of the aromatic heterocyclic group or fused aromaticheterocyclic group having 2 to 30 ring carbon atoms are a pyroryl group,pyrazinyl group, pyridinyl group, indolyl group, isoindolyl group, furylgroup, benzofuranyl group, isobenzofuranyl group, dibenzofuranyl group,dibenzothiophenyl group, quinolyl group, isoquinolyl group, quinoxalinylgroup, carbazolyl group, phenantridinyl group, acridinyl group,phenanthrolinyl group, thienyl group and a group formed from a pyridinering, pyrazine ring, pyrimidine ring, pyridazine ring, triazine ring,indol ring, quinoline ring, acridine ring, pirrolidine ring, dioxanering, piperidine ring, morpholine ring, piperadine ring, carbazole ring,furan ring, thiophene ring, oxazole ring, oxadiazole ring, benzooxazolering, thiazole ring, thiadiazole ring, benzothiazole ring, triazolering, imidazole ring, benzoimidazole ring, pyrane ring and dibenzofuranring. Among the above, the aromatic heterocyclic group or fused aromaticheterocyclic group having 2 to 10 ring carbon atoms is preferable.

Examples of the aromatic hydrocarbon group or fused aromatic hydrocarbongroup having 6 to 30 ring carbon atoms are a phenyl group, naphthylgroup, phenanthryl group, biphenyl group, terphenyl group, quarterphenylgroup, fluoranthenyl group, triphenylenyl group, phenanthrenyl group,pyrenyl group, chrysenyl group, fluorenyl group, and9,9-dimethylfluorenyl group. Among the above, the aromatic hydrocarbongroup or fused aromatic hydrocarbon group having 6 to 20 ring carbonatoms is preferable.

When A₁, A₂, X₁, X₂ and Y₁ to Y₅ in the formula (1A) or (2A) each haveone or more substituents, the substituents are preferably a linear,branched or cyclic alkyl group having 1 to 20 carbon atoms; linear,branched or cyclic alkoxy group having 1 to 20 carbon atoms; linear,branched or cyclic haloalkyl group having 1 to 20 carbon atoms; linear,branched or cyclic alkylsilyl group having 1 to 10 carbon atoms;arylsilyl group having 6 to 30 ring carbon atoms; cyano group; halogenatom; aromatic hydrocarbon group or fused aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms; or aromatic heterocyclic group orfused aromatic heterocyclic group having 2 to 30 ring carbon atoms.

Examples of the linear, branched or cyclic alkyl group having 1 to 20carbon atoms; linear, branched or cyclic alkoxy group having 1 to 20carbon atoms; linear, branched or cyclic haloalkyl group having 1 to 20carbon atoms; linear, branched or cyclic alkylsilyl group having 1 to 10carbon atoms; arylsilyl group having 6 to 30 ring carbon atoms; aromatichydrocarbon group or fused aromatic hydrocarbon group having 6 to 30ring carbon atoms: and aromatic heterocyclic group or fused aromaticheterocyclic group having 2 to 30 ring carbon atoms are theabove-described groups. The halogen atom is exemplified by a fluorineatom.

Examples of compounds for the biscarbazole derivative according to thisexemplary embodiment represented by the formula (1A) or (2A) are asfollows:

The biscarbazole derivative according to this exemplary embodimentrepresented by the formula (1A) or (2A) is a biscarbazole derivative inwhich carbazole skeletons are bonded to each other respectively at asecond position and a third position. In general, a reaction activeposition of carbazole is a third position, not a second position. Forthis reason, synthesis of carbazole derivatives having a substituent ata second position is more difficult than synthesis of carbazolederivatives having a substituent at a third position, e.g., synthesis ofa biscarbazole derivative in which carbazole skeletons are bonded toeach other at their third positions. In this exemplary embodiment, thesecompounds are synthesized by a method described in Example describedlater.

The organic EL device according to this exemplary embodiment maypreferably contain the electron injecting/transporting layer thatcontains the biscarbazole derivative compound.

The organic EL device according to this exemplary embodiment maypreferably contain at least one of the electron injecting/transportinglayer and the hole blocking layer that contains the biscarbazolederivative compound.

The organic EL device according to this exemplary embodiment maypreferably include the hole transporting layer (hole injecting layer)that contains the biscarbazole derivative compound.

The carbazole derivative represented by the formula (1A) or (2A)according to this exemplary embodiment tends to have a smallerionization potential (IP) than, for instance, a biscarbazole derivativein which carbazole skeletons are bonded to each other at their thirdpositions. When the carbazole derivative according to this exemplaryembodiment is used as an organic-EL-device material, the carbazolederivative is expected to have a higher hole injectivity.

Moreover, in the biscarbazole derivative, to change a bonding positionbetween carbazoles means to change a conjugated system. For instance,when a biscarbazole derivative in which carbazole skeletons are bondedto each other at their third positions is changed to the carbazolederivative according to the exemplary embodiment of the invention inwhich carbazole skeletons are bonded to each other respectively at asecond position and a third position, a conjugated system is cut off toincrease a singlet energy gap (Sl) and lower affinity (Af). Accordingly,it is expected that such a change of the bonding position from the thirdpositions to the second and third positions enables control of electroninjectability into the carbazole derivative.

The invention presented in the present disclosure provides a novelcombination of one or more emitter host materials and a phosphorescentdopant material. The one or more emitter host material comprises one ormore of biscarbazole derivative material having a hole transportingcapability and an electron transporting capability and exhibiting anexcellent carrier balance. The organic EL device made with thecombination of emitter host and phosphorescent dopant materials exhibitlow operational voltage and enhanced lifetime. The inventors achievedthese enhancements after a dedicated study. The inventors found that acompound including two carbazolyl groups and a nitrogen-containingheterocyclic group effectively works for optimizing a carrier balance inthe emitting layer of an organic EL device when used as a host materialin the emitter layer of the device.

However, as mentioned previously above, a luminous efficiency andlifetime of multilayered organic EL devices depend on a carrier balanceof the entire organic EL device. The main factors for controlling thecarrier balance are carrier transporting capability of each of theorganic layers and carrier injecting capability in the interfacialregion of separate organic layers. In order to balance the carrierinjecting capability to neighboring layers in the emitting layer(recombination region), it is preferable to adjust the carrier balanceby a plurality of host materials. Specifically, it is preferable that,in addition to the first host material, the second host material issuitably selected as a co-host in the emitting layer. The co-host systemof the combinations disclosed herein were found to provide suchenhancements.

[Synthesis of Host Material Compound 1C]:

A synthesis scheme of Compound 1C is shown below.

3-bromobenzaldehydro (100 g, 54 mmol) and aniline (50 g, 54 mmol) wereadded to toluene (1 L) and heated to reflux for 8 hours. After thereaction solution was cooled down, a solvent was concentrated underreduced pressure to obtain an intermediate body 1C-1 (130 g, a yield of93%).

Subsequently, under an argon gas atmosphere, the intermediate body 1C-1(130 g, 50 mmol), benzamidine hydrochloride (152 g, 100 mmol), anhydrousethanol (1 L), and sodium hydroxide (42 g) were added together insequential order, and stirred at 80 degrees C. for 16 hours.Subsequently, sodium-t-butoxide (20 g, 208 mmol) were further added andheated at 80 degrees C. for 16 hours with stirring. After the reactionsolution was cooled down, a solid was separated by filtration and washedwith methanol to obtain an intermediate body 1C-2 (67 g, a yield of37%).

Under an argon gas atmosphere, the intermediate body 1-4 (1.6 g, 3.9mmol), the intermediate body 1C-2 (1.5 g, 3.9 mmol),tris(dibenzylideneacetone)dipalladium (0.071 g, 0.078 mmol),tri-t-butylphosphonium tetrafluoroborate (0.091 g, 0.31 mmol), sodiumt-butoxide (0.53 g, 5.5 mmol), and anhydrous toluene (20 mL) weresequentially mixed, and heated to reflux for 8 hours.

After the reaction solution was cooled down to the room temperature, anorganic layer was removed and an organic solvent was distilled awayunder reduced pressure. The obtained residue was refined by silica-gelcolumn chromatography, whereby a compound 1C (2.3 g, a yield of 82%) wasobtained.

FD-MS analysis consequently showed that m/e was equal to 715 while acalculated molecular weight was 715.

[Synthesis of Host Material Compound 2C]:

A synthesis scheme of the compound 2C is shown below.

Under a nitrogen atmosphere, trichloropyrimidine (10 g, 54.5 mmol),phenylboronic acid (13.3 g, 109 mmol), palladium acetate (0.3 g, 1.37mmol), triphenylphosphine (0.72 g, 2.73 mmol), dimethoxyethane (150 mL)and an aqueous solution of 2M sodium carbonate (170 mL) were addedtogether in sequential order, and heated to reflux for 8 hours.

After the reaction solution was cooled down to the room temperature, anorganic layer was removed and an organic solvent was distilled awayunder reduced pressure. The obtained residue was refined by silica-gelcolumn chromatography, whereby an intermediate body 2C-1 (9.2 g, a yieldof 63%) was obtained

Under a nitrogen atmosphere, 2-nitro-1,4-dibromobenzene (11.2 g, 40mmol), phenylboronic acid (4.9 g, 40 mmol),tetrakis(triphenylphosphine)palladium (1.39 g, 1.2 mmol), toluene (120mL) and an aqueous solution of 2M sodium carbonate (60 mL) were addedtogether in sequential order, and heated to reflux for 8 hours.

After the reaction solution was cooled down to the room temperature, anorganic layer was removed and an organic solvent was distilled awayunder reduced pressure. The obtained residue was refined by silica-gelcolumn chromatography, whereby an intermediate body 2C-2 (6.6 g, a yieldof 59%) was obtained.

Subsequently, under an argon gas atmosphere, the intermediate body 7-2(6.6 g, 23.7 mmol), triphenylphosphine (15.6 g, 59.3 mmol), ando-dichlorobenzene (24 mL) were added together in sequential order, andheated to reflux at 180 degrees C. for 8 hours.

After cooled down to the room temperature, the reaction solution wasrefined by silica-gel column chromatography, whereby an intermediatebody 2C-3 (4 g, a yield of 68%) was obtained.

Under a nitrogen atmosphere, the intermediate body 2C-3 (4 g, 16 mmol),N-phenylcarbazolyl-3-boronic acid (5.1 g, 17.8 mmol),tetrakis(triphenylphosphine)palladium (0.56 g, 0.48 mmol), toluene (50mL) and an aqueous solution of 2M sodium carbonate (24 mL) were addedtogether in sequential order, and heated to reflux for 8 hours.

After the reaction solution was cooled down to the room temperature, anorganic layer was removed and an organic solvent was distilled awayunder reduced pressure. The obtained residue was refined by silica-gelcolumn chromatography, whereby an intermediate body 2C-4 (3.2 g, a yieldof 49%) was obtained.

Under an argon gas atmosphere, the intermediate body 2C-4 (1.6 g, 3.9mmol), the intermediate body 2C-1 (1.0 g, 3.9 mmol),tris(dibenzylideneacetone)dipalladium (0.071 g, 0.078 mmol),tri-t-butylphosphonium tetrafluoroborate (0.091 g, 0.31 mmol), sodiumt-butoxide (0.53 g, 5.5 mmol), and anhydrous toluene (20 mL) weresequentially mixed, and heated to reflux for 8 hours.

After the reaction solution was cooled down to the room temperature, anorganic layer was removed and an organic solvent was distilled awayunder reduced pressure. The obtained residue was refined by silica-gelcolumn chromatography, whereby a compound 2C (2.4 g, a yield of 95%) wasobtained.

FD-MS analysis consequently showed that m/e was equal to 638 while acalculated molecular weight was 638.

[Synthesis of the Host Material Compound 3B]:

A synthesis scheme of the Compound 3B is shown below.

Under an argon atmosphere, toluene (150 mL), dimethoxyethane (150 mL),and an aqueous solution of sodium carbonate having a concentration of 2M (150 mL) were added to 4-iodobromobenzene (28.3 g, 100.0 mmol),dibenzofuran-4-boronic acid (22.3 g, 105 mmol), andtetrakis(triphenylphosphine)palladium(0) (2.31 g, 2.00 mmol), and thenthe mixture was heated for 10 hours while being refluxed.

Immediately after the completion of the reaction, the resultant wasfiltrated, and then the aqueous layer was removed. The organic layer wasdried with sodium sulfate, and was then concentrated. The residue waspurified by silica gel column chromatography. Thus, an intermediate body3B-1 (26.2 g, 81% yield) was obtained. FD-MS (field desorption massspectrometry) analysis confirmed that the intermediate had a ratio m/eof 322 with respect to its molecular weight, i.e., 322.

Under an argon atmosphere, the intermediate body 3B-1 (2.36 g, 7.3mmol), an intermediate body 3B-2 (3.0 g, 7.3 mmol), CuI (1.4 g, 7.3mmol), tripotassium phosphate (2.3 g, 11 mmol), anhydrous dioxane (30mL), and cyclohexanediamine (0.84 g, 7.3 mmol) were loaded in the statedorder into a three-necked flask, and were then stirred at 100° C. for 8hours.

Water was added to the reaction liquid to precipitate a solid, and thenthe solid was washed with hexane and then with methanol. Further, theresultant solid was purified by silica gel column chromatography. Thus,a compound 3B (2.9 g, 60% yield) was obtained. The result of FD-MSanalysis confirmed that the compound had a ratio m/e of 650 with respectto its molecular weight, i.e., 650.

[Example Synthesis Information for the Phosphorescent Compound 4B]:

The phosphorescent dopant Compound 4B was synthesized as follows:

A mixture was prepared of 2,4-dibromopyridine (10 g, 42.21 mmol),phenylboronic acid (5.1 g, 42.21 mmol), and potassium carbonate (11.7 g,84.42 mmol) in 100 mL dimethoxyethane and 40 mL of water. Nitrogen wasbubbled directly into the mixture for 30 minutes. Next,tetrakis(triphenylphosphine)palladium(0) was added (244 mg, 2.11 mmol)and the mixture was heated to reflux under nitrogen overnight. Themixture was cooled and diluted with ethyl acetate and water. The layerswere separated and the aqueous layer was extracted with ethyl acetate.The organic layers were washed with brine, dried over magnesium sulfate,filtered, and evaporated to a residue. The residue was purified bycolumn chromatography eluting with 0, 2, and 5% ethyl acetate/hexanes.Obtained 4.28 g of a yellow liquid (43%).

Synthesis of2-phenyl-4(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2yl)pyridine

A mixture was prepared of 2-phenyl-4-bromopyridine (4.28 g, 18.28 mmol),bis(pinacolato)diboron (9.29 g, 36.57 mmol), and potassium acetate (5.38g, 54.84 mmol) in 100 mL of dioxane. Nitrogen was bubbled directly intothe mixture for 30 minutes.Dichloro[1,1′-ferrocenylbis(diphenylphosphine)]palladium(II)dichloromethane (448 mg, 0.55 mmol) was added, and nitrogen was bubbledfor another 15 minutes. The reaction mixture was heated to 90° C.internally. After 1 h, the reaction was complete, and the heat was shutoff. The solvent was evaporated to an oil. The oil was purified byKugelrohr at 200° C. to remove excess bis(pinacolato)diboron. Theresidue left in the boiling pot was dissolved in ethyl acetate andfiltered through magnesium sulfate, rinsed with ethyl acetate, and thefiltrate was evaporated. Used as described in the next step. Yield wasapproximately 4 g of product.

Synthesis of PPY Dimer

14.7 g (0.04 mol) of iridium chloride and 26.0 g (0.17 mol) of2-phenylpyridine was placed in a 1 L round bottomed flask. 300 ml of2-ethocyethanol and 100 ml of water was added. The mixture was refluxedunder nitrogen atmosphere overnight. After having cooled to roomtemperature, the precipitate was filtered and washed with methanol.After drying, 22 g of dimer was obtained. (99% yield).

Synthesis of Triflate

22 g of dimer was dissolved in 1 L of dichloromethane. 10.5 g (0.04 mol)of silver triflate was added to the solution. 25 ml of methanol was thenadded. The solution was stirred for 5 h. The silver chloride wasfiltered off. The solvent was evaporated. 26 g of product was obtained.The solid was used for next step without further purification.

Synthesis of Boronic Ester Precursor

A mixture was prepared of the triflate (4.6 g, 7.11 mmol) and2-phenyl-4(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2yl)pyridine (˜4 g,−14.23 mmol) in 100 mL of ethanol. The mixture was heated at reflux for6 h under nitrogen. The solvent was evaporated and hexanes was added. Asold was filtered off which was washed with hexanes. The solid waspurified by column chromatography eluting with dichloromethane and latersome methanol was added. Obtained 0.92 g of an orange solid(approximately 17%).

Synthesis of Compound 4B

Mixed the boronic ester precursor (0.92 g, 1.18 mmol), bromobenzene (0.6g, 3.54 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (19 mg,0.047 mmol), and potassium phosphate tribasic (0.82 g, 3.54 mmol) in 50mL of tolune and 5 mL of water. Bubbled nitrogen directly into themixture for 30 minutes after whichtris(dibenzylideneacetone)dipalladium(0) (11 mg, 0.0118 mmol) was added.Nitrogen was bubbled for another 5 minutes then the reaction mixture washeated to reflux for 1 h under nitrogen. The mixture was cooled and anorange solid precipitated out. The solid was filtered off and washedwith hexanes followed by methanol. Some solid was seen in filtrate sothe filtrate was evaporated and methanol was added. More orange solidwas filtered off. All the solid was purified by column chromatographyeluting with 50% dichloromethane/hexanes. The solid was sublimed at28O<0>C. Obtained 0.53 g (62%).

[Device Data]

The invention will be described in further detail with reference to someexample devices and reference devices. However, the invention is notlimited by the description of the examples.

[Manufacture of Organic EL Device Having Single Host—Example Device #1]

A glass substrate (size: 25 mm×75 mm×1.1 mm) having an ITO transparentelectrode (manufactured by Geomatec Co., Ltd.) was ultrasonic-cleaned inisopropyl alcohol for five minutes, and then UV(Ultraviolet)/ozone-cleaned for 30 minutes.

After the glass substrate having the transparent electrode was cleaned,the glass substrate was mounted on a substrate holder of a vacuumdeposition apparatus. A hole injection layer was initially formed byvapor-depositing a 5 nm thick Compound HI to cover the surface of theglass substrate where a transparent electrode line was provided. A holetransporting layer was formed by sequentially vapor-depositing a 50 nmthick Compound HT-1 and 10 nm thick Compound HT-2 over the electronblocking layer.

A phosphorescence-emitting layer was obtained by co-depositing theCompound 1C used as a phosphorescent host material and Compound 4B usedas a phosphorescent dopant material onto the hole transporting layer ina thickness of 40 nm. The concentration of Compound 4B was 10 mass %.

Subsequently, a 30 nm thick electron transporting layer of Compound ET,a 1 nm thick LiF layer and a 80 nm thick metal Al layer weresequentially formed to obtain a cathode. A LiF layer, which is anelectron injectable electrode, was formed at a speed of 1 Å/min.

[Manufacture of Organic EL Device Having Single Host—Example Device #2]

The Example Device #2 was prepared in the same manner as Example Device#1 except that Compound 2C was used as the phosphorescent host materialinstead of Compound 1C.

[Manufacture of Organic EL Device Having Single Host—Reference Device#1]

The Reference Device #1 was prepared in the same manner as ExampleDevice #1 except that CBP (4,4′-bis(N-carbazolyl)biphenyl) was use asthe phosphorescent host material instead of Compound 1C.

[Manufacture of Organic EL Device Having Single Host—Reference Device#2]

The Reference Device #2 was prepared in the same manner as ExampleDevice #1 except that Ir(bzq)₃ was use as the phosphorescent dopantmaterial instead of Compound 4B.

[Manufacture of Organic EL Device Having Single Host—Reference Device#3]

The Reference Device #3 was prepared in the same manner as ExampleDevice #2 except that Ir(bzq)₃ was use as the phosphorescent dopantmaterial instead of Compound 4B.

[Manufacture of Organic EL Device Having Single Host—Reference Device#4]

The Reference Device #4 was prepared in the same manner as ReferenceDevice #1 except that Ir(bzq)₃ was use as the phosphorescent dopantmaterial instead of Compound 4B.

[Manufacture of Organic EL Device Having Co-Host—Example Device #3]

A glass substrate (size: 25 mm×75 mm×1.1 mm) having an ITO transparentelectrode (manufactured by Geomatec Co., Ltd.) was ultrasonic-cleaned inisopropyl alcohol for five minutes, and then UV(Ultraviolet)/ozone-cleaned for 30 minutes.

After the glass substrate having the transparent electrode was cleaned,the glass substrate was mounted on a substrate holder of a vacuumdeposition apparatus. A hole injection layer was initially formed byvapor-depositing a 5 nm thick Compound HI to cover the surface of theglass substrate where a transparent electrode line was provided. A holetransporting layer was formed by sequentially vapor-depositing a 50 nmthick Compound HT-1 and 10 nm thick Compound HT-2 over the electronblocking layer.

A phosphorescence-emitting layer was obtained by co-depositing theCompounds 1C and 2C used as phosphorescent co-host materials andCompound 4B used as a phosphorescent dopant material onto the holetransporting layer in a thickness of 40 nm. The concentration ofCompound 4B was 10 mass % and the concentration of the co-host compounds1C and 2C were 45 mass % each.

Subsequently, a 30 nm thick electron transporting layer of Compound ET,a 1 nm thick LiF layer and a 80 nm thick metal Al layer weresequentially formed to obtain a cathode. A LiF layer, which is anelectron injectable electrode, was formed at a speed of 1 Å/min.

[Manufacture of Organic EL Device Having Co-Hosts—Example Device #4]

The Example Device #4 was prepared in the same manner as Example Device#3 except that Compounds 1C and 3B were used as the phosphorescentco-host materials.

[Manufacture of Organic EL Device Having Co-Hosts—Reference Device #5]

The Reference Device #5 was prepared in the same manner as ExampleDevice #3 except that Compounds 1C and CBP were used as thephosphorescent co-host materials.

[Manufacture of Organic EL Device Having Co-Hosts—Reference Device #6]

The Reference Device #6 was prepared in the same manner as ExampleDevice #3 except that Ir(bzq)₃ was used as the phosphorescent dopantmaterial instead of Compound 4B.

[Manufacture of Organic EL Device Having Co-Hosts—Reference Device #7]

The Reference Device #7 was prepared in the same manner as ExampleDevice #4 except that Ir(bzq)₃ was used as the phosphorescent dopantmaterial instead of Compound 4B.

[Manufacture of Organic EL Device Having Co-Hosts—Reference Device #8]

The Reference Device #8 was prepared in the same manner as ReferenceDevice #5 except that Ir(bzq)₃ was used as the phosphorescent dopantmaterial instead of Compound 4B.

[Sample Devices]

Table 1 shows the organic compounds used for the emitter dopant materialand the emitter host materials in the manufacture of the Example Devicesand Reference Devices evaluated by the inventors.

TABLE 1 Devices Emitter Dopant Emitter Host 1 Emitter Host 2 Single Hostdevices Example Device #1 Compound 4B Compound 1C — Example Device #2Compound 4B Compound 2C — Reference Device #1 Compound 4B CBP —Reference Device #2 Ir(bzq)₃ Compound 1C — Reference Device #3 Ir(bzq)₃Compound 2C — Reference Device #4 Ir(bzq)₃ CBP — Co-host devices ExampleDevice #3 Compound 4B Compound 1C Compound 2C Example Device #4 Compound4B Compound 1C Compound 3B Reference Device #5 Compound 4B Compound 1CCBP Reference Device #6 Ir(bzq)₃ Compound 1C Compound 2C ReferenceDevice #7 Ir(bzq)₃ Compound 1C Compound 3B Reference Device #8 Ir(bzq)₃Compound 1C CBP

[Evaluation of Sample Devices]

The example organic EL devices manufactured as Example Devices #1 to #4and Reference Devices #1 to #8 were driven by direct-current electricityof 1 mA/cm² to emit light. The emission chromaticity (CIE), theluminescence (L) and the voltage (V) were measured. Using the measuredvalues, the current efficiency (L/J), luminous efficiency η (lm/W) andexternal quantum efficiency (EQE) where obtained. The results are shownin Tables 2, 3 and 4.

Table 2 shows the LT80 life time data for Example Devices #3 and #4having two host materials in the emitter layer according to an aspect ofthe present disclosure.

TABLE 2 CIE @ voltage @ EQE @ LT80 @ 10 mA/cm² 10 mA/cm² 10 mA/cm² 50mA/cm² x y [V] [%] [hrs] Example 0.435 0.552 3.76 18.8 658* Device #3Example 0.435 0.553 3.97 21.5 470* Device #4 Reference 0.432 0.555 3.8618.8 — Device #5 *extrapolated data

TABLE 3 Single host devices Current LT80 @ Sample Density volt. L/J ηEQE CIE λp 25,000 cd/m² Device (mA/cm²) (V) (cd/A) (Im/W) (%) x y (nm)(hrs) Example 1 2.64 78.1 92.8 23.1 0.441 0.548 557 190 Device #1 103.30 67.7 64.4 19.9 0.438 0.551 556 Example 1 2.91 75.6 81.8 22.3 0.4410.558 557 640 Device #2 10 3.75 69.4 58.2 20.4 0.439 0.549 557 Reference1 4.42 32.8 23.3 9.6 0.438 0.549 557 200 Device #1 10 5.67 48.7 27.014.3 0.440 0.549 556 Reference 1 3.09 63.1 64.2 18.6 0.452 0.540 556 110Device #2 10 3.76 52.7 44.1 15.6 0.452 0.541 556 Reference 1 3.00 56.559.2 16.8 0.457 0.536 558 390 Device #3 10 3.86 49.7 40.4 14.8 0.4560.536 557 Reference 1 4.23 22.2 16.5 6.5 0.448 0.533 555 110 Device #410 5.11 39.0 24.0 11.4 0.449 0.543 556 Example 1 2.87 73.7 80.7 21.70.438 0.551 555 650 Device #3 10 3.76 64.2 53.7 18.8 0.435 0.552 555Example 1 3.04 81.0 83.6 23.7 0.437 0.552 555 810 Device #4 10 3.97 73.958.4 21.5 0.435 0.553 555 Reference 1 2.98 77.4 81.5 22.6 0.435 0.553555 300 Device #5 10 3.86 64.5 52.4 18.8 0.432 0.555 554 Reference 12.83 60.0 66.7 17.4 0.444 0.548 554 350 Device #6 10 3.66 50.6 43.4 14.60.443 0.548 554 Reference 1 3.16 60.6 60.2 17.5 0.445 0.547 554 350Device #7 10 4.03 54.1 42.1 15.6 0.443 0.548 554 Reference 1 3.37 64.159.7 18.8 0.450 0.542 556 290 Device #8 10 4.24 55.4 41.0 16.2 0.4490.543 556

[Table 4] Co-Host Devices

Table 3 shows the performance parameters of the single-host devices,Example Devices #1 and #2 in comparison to the Reference Devices #1 to#4. The data compares the performance of the combinations of thephosphorescent Compound 4B with the host Compounds 1C and 2C against theperformance of the combination of materials in the Reference Devices.FIGS. 2-5 also show plots of the device performance parameters comparingthe Example Devices #1, #2 to the Reference Devices #1 to #4.

Comparing the Example Device #1 and the Reference Device #2, thecombination of the host material Compound 1C and the phosphorescentdopant Compound 4B in Example Device #1 resulted in lower voltage,longer lifetime, higher L/J and external quantum efficiency (EQE) thanthe combination of host material Compound 1C and phosphorescent dopantIr(bzq)₃ of the Reference Device #2 at 1 mA/cm² and at 10 mA/cm².

Similarly, the combination of the host material Compound 2C and thephosphorescent dopant Compound 4B in Example Device #2 resulted in lowervoltage, longer lifetime, higher L/J and EQE than the combination of thehost material Compound 2C and phosphorescent dopant Ir(bzq)₃ of theReference Device #3 at 1 mA/cm² and at 10 mA/cm².

The lifetime plot (LT80 plot) shown in FIG. 5 show that the ExampleDevices #1 and #2 demonstrate substantially longer lifetime compared tothe Reference Devices #1, #2, #3, and #4.

The data in Table 3 and FIG. 5 also show that the phosphorescentCompound 4B has lower voltage, longer lifetime, higher L/J, and EQE thanIr(bzq)₃.

Thus, the phosphorescent Compound 4B as an emitter and Compounds 1C or2C as a host material in the emitter region produces more efficientluminance and electrochemically more robust than conventional materials,such as Ir(bzq)₃ and CBP, in PHOLED devices.

Table 4 shows the performance parameters of the co-host devices, ExampleDevices #3 and #4 and the Reference Devices #5 to #8. The data comparesthe performance of the phosphorescent Compound 4B in combination withco-host systems, Compound 1C & 2C and Compound 1C & 3B against theperformance of the combination of materials in the Reference Devices #5to #8. FIGS. 6-9 also show plots of the device performance parameterscomparing the Example Devices #3, #4 to the Reference Devices #5 to #8.

Comparing the Example Device #3 and the Reference Device #6, thecombination of the phosphorescent Compound 4B with co-host Compounds 1C& 2C resulted in lower voltage, longer lifetime, higher L/J, and EQEthan the combination of the phosphorescent dopant Ir(bzq)₃ with theco-host Compounds 1C & 2C at 1 mA/cm² and at 10 mA/cm².

Comparing the Example Device #4 and the Reference Device #7, thecombination of the phosphorescent Compound 4B with co-host Compounds 1C& 3B resulted in lower voltage, longer lifetime, higher L/J, and EQEthan the combination of the phosphorescent Ir(bzq)₃ with the co-hostCompounds 1C & 3B at 1 mA/cm² and at 10 mA/cm².

The lifetime plot (LT80 plot) shown in FIG. 9 show that the ExampleDevices #3 and #4 demonstrate substantially longer lifetime compared tothe Reference Devices #5, #6, #7, and #8.

The Tables 3 and 4 also show the LT80 data of the Example Devices #1,#2, #3, and #4 and the Reference Devices #1, #2, #3, #4, #5, #6, #7, and#8. The Example devices exhibit longer lifetime than the Referencedevices. And among the Example devices that comprise the host and dopantmaterial combinations according to the present disclosure, the co-hostExample Devices #3 and 4 have longer lifetime than the single hostExample Devices #1 and #2. As discussed above, the inventors believethat this is because the co-host material combinations disclosed hereinimproves the carrier injecting capability to neighboring layers in theemitting layer (recombination region).

The above device data show that when the biscarbazole derivativecompounds of the present disclosure are used, either as a single host orpaired as co-hosts, in combination with the phosphorescent material ofthe family represented by compound formula 4A, such as Compound 4B, in aPHOLED, those combinations perform superior to PHOLED devices made frommaterial combinations that contain the biscarbazole derivative compoundswith a different phosphorescent dopant (e.g. Ir(bzq)₃) or thephosphorescent dopant compound of formula 4A with different hostcompounds (e.g. CBP).

The inventors believe that the combinations of the phosphorescentCompound 4B with the host material Compounds 1C, 2C, or 3B enhancedevice performance by improving charge balance and recombination. Thedevice data discussed above show that the host material Compound 2C withphosphorescent Compound 4B is superior to the Reference Device examplesin terms of voltage, luminous efficacy and lifetime.

What is claimed is:
 1. An organic electroluminescence device comprising:a cathode; an anode; and a plurality of organic thin-film layersprovided between the cathode and the anode, the plurality of organicthin-film layers comprising an emitting layer, wherein at least one ofthe plurality of organic thin-film layers is the emitting layercomprising a phosphorescent material and a host material that is abiscarbazole derivative compound represented by a formula (1A) or (2A)below:

wherein A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 carbon atoms forming a ring; A₂represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, or substituted or unsubstitutednitrogen-containing heterocyclic group having 1 to 30 ring carbon atoms;X₁ and X₂ each independently represents substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms; Y₁ to Y₄independently represent a hydrogen atom, fluorine atom, cyano group,substituted or unsubstituted alkyl group having 1 to 20 carbon atoms,substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms,substituted or unsubstituted haloalkyl group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkoxy group having 1 to 20carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms; adjacent ones of Y₁ to Y₄ are allowedto be bonded to each other to form a ring structure; p and q representan integer of 1 to 4; r and s represent an integer of 1 to 3; and when pand q are an integer of 2 to 4 and r and s are an integer of 2 to 3, aplurality of Y₁ to Y₄ are allowed to be the same or different; whereinthe phosphorescent material is an organometallic compound having asubstituted chemical structure represented by the following formula(4A):

wherein each R is independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl, heteroaryl,substituted aryl, substituted heteroaryl or a heterocyclic group; M is aplatinum group metal; Ar′, Ar″, Ar′″ and Ar″″ each independentlyrepresent a substituted or unsubstituted aryl or heteroaryl substituenton the phenylpyridine ligand; a is 0 or 1; b is 0 or 1; c is 0 or 1; dis 0 or 1; m is 1 or 2; n is 1 or 2; m+n is the maximum number ofligands that can be coordinated to M, and wherein at least one of a, b,c, and d is 1 and when at least one of a and b is 1 and at least one ofb and c is 1, at least one of Ar′ and Ar″ is different from at least oneof Ar′″ and Ar″″.
 2. The device according to claim 1, wherein thephosphorescent material is a compound represented by the followingformula (4B):


3. The device according to any one of claims 1 to 2, wherein the A₁represents a substituted or unsubstituted benzofuranyl group, asubstituted or unsubstituted dibenzofuranyl group, a substituted orunsubstituted benzothiophenyl group, a substituted or unsubstituteddibenzothiophenyl group, a substituted or unsubstitutedbenzonaphthofuranyl group, or a substituted or unsubstitutedbenzonaphthothiophenyl group.
 4. The device according to claim 1,wherein M is a metal atom selected from iridium (Ir), Osmium (Os), andplatinum (Pt).
 5. The device according to claim 1, wherein the hostmaterial is a biscarbazole derivative compound represented by a formula(1C) or (2C) below:


6. A lighting apparatus, comprising the organic electroluminescencedevice according to claim
 1. 7. A display apparatus, comprising theorganic electroluminescence device according to claim
 1. 8. An organicelectroluminescence device comprising: a cathode; an anode; and aplurality of organic thin-film layers provided between the cathode andthe anode, the organic thin-film layers comprising an emitting layer,wherein at least one of the plurality of organic thin-film layers is theemitting layer comprising a first host material, a second host materialand a phosphorescent material providing phosphorescence, the first hostmaterial being a biscarbazole derivative compound represented by aformula (1A) below:

wherein A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms; A₂ represents asubstituted or unsubstituted aromatic hydrocarbon group having 6 to 30ring carbon atoms, or substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms; X₁ and X₂ eachindependently represents substituted or unsubstituted aromatichydrocarbon group having 6 to 30 ring carbon atoms, substituted orunsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms; Y₁ to Y₄independently represent a hydrogen atom, fluorine atom, cyano group,substituted or unsubstituted alkyl group having 1 to 20 carbon atoms,substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms,substituted or unsubstituted haloalkyl group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkoxy group having 1 to 20carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms; adjacent ones of Y₁ to Y₄ are allowedto be bonded to each other to form a ring structure; p and q representan integer of 1 to 4; r and s represent an integer of 1 to 3; when p andq are an integer of 2 to 4 and r and s are an integer of 2 to 3, aplurality of Y₁ to Y₄ are allowed to be the same or different; thesecond host material being a biscarbazole derivative compoundrepresented by a formula (2A) below:

wherein X₂ represents a single bond, substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms; Y₁ to Y₄independently represent a hydrogen atom, fluorine atom, cyano group,substituted or unsubstituted alkyl group having 1 to 20 carbon atoms,substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms,substituted or unsubstituted haloalkyl group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkoxy group having 1 to 20carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms; adjacent ones of Y₁ to Y₄ are allowedto be bonded to each other to form a ring structure; p and q representan integer of 1 to 4; r and s represent an integer of 1 to 3; and when pand q are an integer of 2 to 4 and r and s are an integer of 2 to 3, aplurality of Y₁ to Y₄ are allowed to be the same or different.
 9. Thedevice according to claim 8, wherein the phosphorescent material is anorganometallic compound having a substituted chemical structurerepresented by the following formula (4A):

wherein each R is independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl, heteroaryl,substituted aryl, substituted heteroaryl or a heterocyclic group; M is aplatinum group metal; Ar′, Ar″, Ar′″ and Ar″″ each independentlyrepresent a substituted or unsubstituted aryl or heteroaryl substituenton the phenylpyridine ligand; a is 0 or 1; b is 0 or 1; c is 0 or 1; dis 0 or 1; m is 1 or 2; n is 1 or 2; m+n is the maximum number ofligands that can be coordinated to M, and wherein at least one of a, b,c, and d is 1 and when at least one of a and b is 1 and at least one ofb and c is 1, at least one of Ar′ and Ar″ is different from at least oneof Ar′″ and Ar″″.
 10. The device according to claim 9, wherein thephosphorescent material is an organometallic compound represented by thefollowing formula (4B) below:


11. The device according to any one of claims 8 to 10, wherein the A₁represents a substituted or unsubstituted benzofuranyl group, asubstituted or unsubstituted dibenzofuranyl group, a substituted orunsubstituted benzothiophenyl group, a substituted or unsubstituteddibenzothiophenyl group, a substituted or unsubstitutedbenzonaphthofuranyl group, or a substituted or unsubstitutedbenzonaphthothiophenyl group.
 12. The device according to claim 9,wherein M is a metal atom selected from iridium (Ir), Osmium (Os), andplatinum (Pt).
 13. The device according to claim 8, wherein the firsthost material is a biscarbazole derivative compound represented by aformula (1C) below:


14. The device of claim 8, wherein the second host material is abiscarbazole derivative compound represented by a formula (2C) below:


15. A lighting apparatus, comprising the organic electroluminescencedevice according to claim
 8. 16. A display apparatus, comprising theorganic electroluminescence device according to claim
 8. 17. An organicelectroluminescence device comprising: a cathode; an anode; and aplurality of organic thin-film layers provided between the cathode andthe anode, the organic thin-film layers comprising an emitting layer,wherein at least one of the organic thin-film layers is the emittinglayer comprising a first host material, a second host material and aphosphorescent material providing phosphorescence, the first hostmaterial being a biscarbazole derivative compound represented by aformula (1A) below:

wherein A₁ represents a substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms; A₂ represents asubstituted or unsubstituted aromatic hydrocarbon group having 6 to 30ring carbon atoms, or substituted or unsubstituted nitrogen-containingheterocyclic group having 1 to 30 ring carbon atoms; X₁ and X₂ each areindependently represents substituted or unsubstituted aromatichydrocarbon group having 6 to 30 ring carbon atoms, substituted orunsubstituted fused aromatic hydrocarbon group having 6 to 30 ringcarbon atoms, substituted or unsubstituted aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms, or substituted or unsubstituted fusedaromatic heterocyclic group having 2 to 30 ring carbon atoms; Y₁ to Y₄independently represent a hydrogen atom, fluorine atom, cyano group,substituted or unsubstituted alkyl group having 1 to 20 carbon atoms,substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms,substituted or unsubstituted haloalkyl group having 1 to 20 carbonatoms, substituted or unsubstituted haloalkoxy group having 1 to 20carbon atoms, substituted or unsubstituted alkylsilyl having 1 to 10carbon atoms, substituted or unsubstituted arylsilyl having 6 to 30carbon atoms, substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, substituted or unsubstituted fusedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, substitutedor unsubstituted aromatic heterocyclic group having 2 to 30 ring carbonatoms, or substituted or unsubstituted fused aromatic heterocyclic grouphaving 2 to 30 ring carbon atoms; adjacent ones of Y₁ to Y₄ are allowedto be bonded to each other to form a ring structure; p and q representan integer of 1 to 4; r and s represent an integer of 1 to 3; when p andq are an integer of 2 to 4 and r and s are an integer of 2 to 3, aplurality of Y₁ to Y₄ are allowed to be the same or different; thesecond host material being a biscarbazole derivative compoundrepresented by a formula (3A) below:

wherein G is substituted or unsubstituted aryl group having 6 to 40carbon atoms, or represented by a formula 3(b) below.

in formula 3(b), * represents link with L³; in formula (3A), X₁ issulfur atom or represents N—R⁹; in formula 3(b), X₂ is sulfur atom orrepresents N—R¹⁰; R¹ to R⁸ each represent independently an alkyl grouphaving 1 to 5 carbon atoms, substituted or unsubstituted cycloalkylgroup having 3 to 6 carbon atoms, substituted or unsubstituted alcoxygroup having 1 to 5 carbon atoms, substituted or unsubstitutedcycloalkoxy group having 3 to 6 carbon atoms, substituted orunsubstituted aryl group having 6 to 18 carbon atoms, substituted orunsubstituted aryloxy group having 6 to 18 carbon atoms, substituted orunsubstituted heteroaryl group having 5 to 18 carbon atoms, substitutedby alkyl group having 1 to 5 carbon atoms or unsubstituted amino group,substituted by alkyl group having 1 to 6 carbon atoms or unsubstitutedsilyl group, a fluoro group or a cyano group. R¹ to R⁸ being optionallybonded to each other to form a ring structure; when G or R¹ to R⁸ have asubstituent, R each represent independently an alkyl group having 1 to 5carbon atoms, cycloalkyl group having 3 to 6 carbon atoms, alcoxy grouphaving 1 to 4 carbon atoms, cycloalkoxy group having 3 to 6 carbonatoms, aryl group having 6 to 18 carbon atoms, aryloxy group having 6 to18 carbon atoms, heteroaryl group having 5 to 18 carbon atoms,substituted by alkyl group having 1 to 5 carbon atoms or unsubstitutedamino group, substituted by alkyl group having 1 to 6 carbon atoms orunsubstituted silyl group, a fluoro group or a cyano group; a, d and feach represent independently an integer of any of 0 to 4, and b, c and eeach represent independently an integer of any of 0 to 3; a sum of a tof is 4 or less; R⁹ to R¹⁰ each represent independently an alkyl grouphaving 1 to 5 carbon atoms, phenyl group, toluyl group, dimethyl phenylgroup, trimethyl phenyl group, biphenyl group, dibenzofuranyl group ordibenzothiophenyl group; g represents an integer of any of 0 to 3, and hrepresents an integer of any of 0 to 4; a sum of g and h is 4 or less;provided that when X¹ and X² are nitrogen, and R⁹ is phenyl group, R¹⁰is not phenyl group; L¹ represents a single bond, a divalent linkagegroup containing N, a divalent linkage group containing O, a divalentlinkage group containing Si, a divalent linkage group containing P, adivalent linkage group containing S, an alkylene group having 1 to 5carbon atoms, cycloalkylene group having 3 to 6 carbon atoms, arylenegroup having 6 to 18 carbon atoms or heteroarylene group having 5 to 18carbon atoms; L² and L³ each represent independently a single bond, analkylene group having 1 to 5 carbon atoms, cycloalkylene group having 3to 6 carbon atoms, arylene group having 6 to 18 carbon atoms orheteroarylene group having 5 to 18 carbon atoms; L¹ to L³ may be furthersubstituted with the substituent R described above; provided that whenL¹ is an arylene group or a heteroarylene group, a and d each representindependently an integer of any of 1 to
 4. 18. The device according toclaim 17, wherein the phosphorescent material is an organometalliccompound having a substituted chemical structure represented by thefollowing formula (4A):

wherein each R is independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl, heteroaryl,substituted aryl, substituted heteroaryl or a heterocyclic group; M is aplatinum group metal; Ar′, Ar″, Ar′″ and Ar″″ each independentlyrepresent a substituted or unsubstituted aryl or heteroaryl substituenton the phenylpyridine ligand; a is 0 or 1; b is 0 or 1; c is 0 or 1; dis 0 or 1; m is 1 or 2; n is 1 or 2; m+n is the maximum number ofligands that can be coordinated to M, and wherein at least one of a, b,c, and d is 1 and when at least one of a and b is 1 and at least one ofb and c is 1, at least one of Ar′ and Ar″ is different from at least oneof Ar′″ and Ar″″.
 19. The device according to claim 18, wherein thephosphorescent material is an organometallic compound represented by thefollowing formula (4B) below:


20. The device according to claim 18, wherein M is a metal atom selectedfrom iridium (Ir), Osmium (Os), and platinum (Pt).
 21. The deviceaccording to claim 17, wherein the first host material is a biscarbazolederivative compound represented by a formula (1B) below:


22. The device of claim 17, wherein the second host material is abiscarbazole derivative compound represented by a formula (3B) below:


23. A lighting apparatus, comprising the organic electroluminescencedevice according to claim
 17. 24. A display apparatus, comprising theorganic electroluminescence device according to claim 17.